#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main()
{
	int n = 0;
	int i = 0;
	double sum = 0;
	for (n = 1; n <= 100; n++)
	{
		i = n % 2;
		if (i == 0)
			sum = sum - 1.0/n;
		else
			sum = sum + 1.0/n;
	}
	printf("%lf", sum);
	return 0;
}